Each year, over a hundred thousand new cases of breast cancer are discovered in women living in the United States. A large percentage of these cases will result in fatalities. One of the most generally accepted methods for treating breast cancer is a lumpectomy, followed by uniform dosage of radiation treatment throughout the breast when cancerous cells remain following surgery. In implementing this method of treatment, it is important to ensure that the radiation received by the breast tissue being treated is uniformly received; due to the detrimental effects of radiation, it is also important to minimize the radiation received by surrounding areas of the body.
Patients treated with radiation therapy often experience varying effects from the radiation treatments. One factor of considerable importance is a patient's body-shape. Certain women, such as those with large, pendulous or irregular shaped breasts, are known to be particularly susceptible to increased toxicities from radiation treatment and poor cosmetic outcomes.
Radiation treatments are most typically carried out with the patient in one of two positions—the supine (face-up) position, or the decubitus (side) position. Both positions have certain advantages and disadvantages. While the supine position is considered more reproducible for providing treatment, particularly with respect to women with large or irregularly shaped breasts, this position results in greater irradiation to surrounding areas such as the lungs and heart and it requires the use of non-homogeneous dose distributions. This is because the transverse displacement of breast tissue over the anterior chest wall that results when a patient is placed in this position creates a large separation resulting in non-uniformity in the dose distribution and the irradiation of large volumes of lung and heart. In order to minimize these problems in women with large or irregularly shaped breasts, when treatment is carried out in the supine position, various modifications to the traditional treatment technique are required. Such modifications include the use of wedge filters, high-energy photon beams, beam-spoilers and bolus.
When used with women with large or irregularly shaped breasts, the decubitus technique is performed with the breast tissue compressed to a greater thickness and, as a result, achieves a more homogeneous dose distribution. However, the decubitus technique requires meticulous patient positioning and protection of the contra-lateral breast; it is also less reproducible and lacks the flexibility that supine position treatment offers.
As an alternative to these more commonly used techniques, it has been determined that the prone position can be used to overcome the limitations of treating women with large or irregularly shaped breasts using the supine and decubitus techniques. The prone position combines the advantage of the decubitus position in providing a homogeneous dose distribution with the reproducibility of the supine position. Use of the prone position also provides several additional notable advantages. Specifically, prone treatment optimizes the shape of the breast with regard to the chest wall for treatment and minimizes the volume of normal tissue (such as the heart, lungs, chest wall and contra-lateral breast tissue) irradiated within the radiation therapy portal during breast treatment. Importantly, various recent studies have concluded that high dose radiation regions are notably reduced for women with large or irregularly shaped breasts using the prone position.
The use of the prone position can not be accomplished using unmodified accelerator tables of traditional linear accelerator machines. These tables have a uniform, flat supporting surface on which the patient is placed for treatment. It will be appreciated by those skilled in the art and familiar with breast radiation therapy equipment, that prone breast treatment can not be performed on accelerator machines of this type without the use of an elevated platform or some other modification because the vertical height adjustment of the accelerator table is limited such that it will not allow the transmission of beam portals underneath the patient supporting surface. Furthermore, the presence of metallic frames at the edges of the patient supporting surface prevents and otherwise interferes with laterally directed radiation portals to a breast suspended from the prone position. There is also no way for the accelerator head to be positioned to irradiate one particular breast without irradiating entire surrounding areas as well. Therefore, in order to properly treat the breast tissue, some modification to, or additional equipment to be used with the traditional accelerator table is required. Modifying the accelerator table itself would be very expensive and difficult to accomplish. Instead, other approaches have focused on providing additional equipment to use in conjunction with the accelerator table.
One such approach known in the art to accomplish breast radiation treatment for a patient in a prone position using a traditional linear accelerator is by placing an elevated therapy platform on top of the linear accelerator table. For example, U.S. Pat. No. 5,564,438, the contents of which are incorporated herein by reference, describes an elevated platform positioned upon a radiation accelerator table of a radiation therapy accelerator machine. The platform described in this patent includes an elevated top surface with an opening through which the breast to be irradiated is inserted to hang freely and pendulously through the platform in an open space treatment field over the top of the accelerator table. Using the elevated table having an opening for the breast, this system attempts to isolate the breast tissue to be irradiated from the rest of the body.
However, this system (and other known systems) have several important limitations. For example, the system described in the '438 Patent does not provide a way to reproducibly position the patient's breast in the opening for treatment.